The development of the South African bitumen-producing industry and the introduction of air-rectified Middle East bitumens is briefly outlined. Reasons for air-rectification of bitumen and manufacturing procedures used by South African refineries are given.

Attention was given in the paper to water quality as it affects the unit operations of water purification. Physical criteria for unit operations selection were put forward. It was suggested that tests to determine the nature of the orthokinetic flocculation be applied. The unit operations reviewed were flocculation, sedimentation and filtration, some aspects of chemical dosing and dispersion were also dealt with. The performance desired and obtained in the unit operations were discussed, and it was concluded that the unit operations approach to water purification is desirable. Functional criteria should be applied in the selection of individual unit operations and to the processes and operations as a whole.